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Question DetailsAsked on 11/11/2016

Enter your question...when we flush the toilet or run the faucet upstairs why can I hear the water drain in the wal

There is a very loud draining noise in the wall when we flush the toilets especially from the 2nd floor. Why?

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2 Answers


Here are links to a few similar questions with answers which might help -

If this is something new, then (assuming you see no leaks anywhere indicating a broken pipe or separated joint) it could mean you have a partial blockage which changes the drainage flow from an even flow in the pipe to a mixture of air and liquid, or causes it to bounce around in the pipe, causing noise. Would take a snaking of thje noisy area from the drain pipe above there to see if that is the source.

Rare, but a blocked vent pipe to the roof can also cause this - usually pouring a 5 gallon bucket of hot water down it will clear it if that is the case. (Make sure you get the vent pipe, not a HVAC vent or duct - will have warm air with sewer smell coming up out of it, and should not have a cap of any kind on it - usually in modern houses 2" PVC or ABS sewer pipe, usually whatever you have in the house for DVW pipe. Can be 2 or 3" galvanized or asbestos or asphaltic composition fiber pipe in older (about pre-80's) houses, or rarely 3 or 4 inch ductile or cast iron all the way to the roof though that is rare in 4 plexes and smaller.

If this is not a new occurrence - perhaps you previously lived in a house with cast iron pipes and this one has plastic - which transmit a LOT more noise - probably about 5-10 times as loud. I have found that PVC drain pipe also generates more complaints then the higher density shiny black ABS DWV pipe.

Another possibility if this is not a new occurrence or you are in a new house so do not know what is "normal" for that house - the plumber did not use expert technique and make sure that no part of the pipes were perfectly vertical - an expert plumber will tilt the "vertical" pipes slightly so the water runs down one side of the pipe consistently - this avoids surging and bouncing from side to side and making noise. (Ditto for gutter downspouts). The vertical runs should be oriented (to maximum extent possible considering pipes may come in to the stack from several sides) so the pipe below Tee or Wye entry points slopes "away" from the pipe entry from fixtures - so the liquid tends to stay in contact with the "bottom" of the pipe as it comes out of the drain, and continue down the same side of the pipe to the next bend. Ideally, the run of near-vertical pipes can be adjusted in mid-run also so not only does incoming flow stay in contact with the pipe, but at the bottom it is running along the side of the pipe thgat is on the "outside" of the curve coming into elbows or tees so it flows smoothly and "with the flow" at tees and wyes without jumping to the other side of the pipe and splashing. Not easy to do with cast or ductile iron - but pretty easy to transition which side of the run is nominally "down" with plastic pipe.

Splashing and gurgling can also be caused by junctions where they used Tee's rather than sanitary tee's or sweep tee's (or wye's) - a LOT of plumbers do this to save a few bucks. Here are images of the difference - you can see as you transition from one to the last, how the flow will be oriented more in line with where it will go after the turn, so it will splash less (ignore the materials or use shown, just picked phtos showing the difference in how the water is turned with the different types of junctions) -

Short of serious replumbing work, about all you can do is, if you find the trouble spot, insulate the wall in that area. Fiberglass preferable because it does not damage the plastic pipe and can easily be removed by a plumber if repairs are needed in the future - but some people do use blown-in cellulose or foam-in-place insulation for this. Particularly common in interior walls where no insulation was put in because of a cheap contractor, so the wall stud cavities are big hollow echo chambers.

Answered 3 years ago by LCD


When you "run" water from a faucet, or just dump dishwater into the drains, the water easily picks up air bubbles when going around corners and thru the traps. It's just about impossible to prevent that "mixing' of air and water as it rushes down the pipes. One way would be to run the faucet slowly to give the water a chance to form a smooth stream. I also live upstairs in a condo, (which is a 1st for me), and I found that dumping my pan of dishwater in the sink will make a racket going down the pipes that the folks below can surely hear, so.... now I just empty the dishpan slowly to create a nice smooth and almost noiseless flow...which only takes a few extra Wife thought this was just genius..... ;-))

Answered 3 years ago by MaineBear

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